As conventional black coloring materials, inorganic pigments such as carbon black and black iron oxide, organic pigments such as aniline black, tar dyestuff such as Black 401, and other various kinds of dyes, are known.
These pigments and dyes, however, do not show a satisfactorily consistent safety, extent of acceptable use, or color value (black value) required as a black coloring material.
Carbon black includes Furnace Black prepared by a continuous incomplete combustion of natural gas, or a petroleum- or coal-derived heavy hydrocarbon oil, in a reaction furnace, and Channel Black prepared by burning natural gas or a hydrocarbon gas with a low flame, bringing the flame into contact with the bottom of a channel steel, resulting in a continuous flame degradation thereof that forms carbon, and recovering the carbon. Furnace Black, however, has been reported to contain benzpyrene, which is a oncogenic substance, and therefore, only Channel Black is used in the cosmetic field in Japan, and both the Channel Black and Furnace Black are prohibited to be used in the United States of America, because they are not safe black coloring materials.
Black iron oxide (FeO.Fe.sub.2 O.sub.3)--also called iron black--does not provide a satisfactory black value when used as a black coloring material.
Organic pigments such as aniline black are not allowed to be used in pharmaceuticals and cosmetics, from the point of view of safety.
Tar dyestuff is considered to be harmful to the human body, and therefore, the extent of the use thereof is severely limited. For example, a tar dyestuff, Black 401 prepared by lake of Naphthol Blue Black with aluminum sulfate cannot be used as a formulation to be coated on the mucous membrane, and thus the use thereof is severely limited. Moreover, Black 401 has other drawbacks in that it has a deficiency in fastness and is slightly water soluble under a neutral condition in comparison with inorganic black coloring materials such as black iron oxide.